Nitride semiconductors are used as light sources of various devices including display devices, signal lamps, lighting devices and optical communication devices. Nitride semiconductors can be used in blue or green light emitting diodes and laser diodes. In addition, nitride semiconductors can also be used in heterojunction bipolar transistors (HBTs), high electron mobility transistors (HEMTs), and the like.
Nitride semiconductors can be grown on a substrate including a sapphire substrate, a silicon carbide substrate or a silicon substrate, in which lattice mismatch occurs. Obtaining lattice-matched substrates tend to be difficult, and the nitride semiconductors grown on a lattice-mismatched substrate have a considerably high threading dislocation density (TDD) of about 1E9/cm2 or more.
Threading dislocation induces non-radiative recombination by providing an electron trap site or provides a current leakage path. When overvoltage such as static electricity is applied to a semiconductor device in such a state, currents are concentrated through the threading dislocations and causes damage to the semiconductor device due to electrostatic discharge (ESD). Thus, the semiconductor device has poor electrostatic characteristics.
Several methods have been proposed to complement poor electrostatic characteristics of nitride semiconductor devices. For example, Zener diodes can be used together with nitride semiconductor devices. The nitride semiconductor devices are protected by connecting the Zener diodes to the nitride semiconductor devices in parallel and diverting unexpected electrostatic discharge to the Zener diodes. However, costs and process time are increased on account of high price and additional processes for Zener diodes.
In another example, a substrate, such as a GaN substrate, lattice-matched with nitride semiconductors can be implemented. However, since the manufacturing costs for the GaN substrate are considerably high, it is difficult to generally apply the GaN substrate to all devices. In fact, the GaN substrate is used for specific devices only such as lasers.
Another possibility is to fill V-pits by growing nitride semiconductor layers having the V-pits in an active layer while adjusting a growth temperature, and growing a p-type semiconductor layer at a high temperature in order to enhance electrostatic discharge characteristics of a nitride semiconductor device. This approach is discussed in KR Patent No. 10-1026031. In this approach, the V-pits formed in the active layer form an electric potential barrier against the injection of carriers, thereby enhancing electrostatic discharge characteristics. However, current leakage can increase according to doping conditions due to a narrow margin for the growth process of the p-type semiconductor layer for filling the V-pits.